1. Field of the Invention
This invention relates to a seal arrangement for rotating shafts, in particular, for the rotating propeller shafts of ships. Propeller shafts can be equipped with at least one ring seal and/or an axial face seal, along with at least one additional backup seal which has an annulus open to the medium in which the propeller is disposed. Along with this annulus, there can also be associated a ring-shaped dirt deflector which creates a backpressure in the annulus when the shaft rotates. To minimize the amount of fine particle contaminants present in the annulus, which particles could eventually pass through the seals of the shaft, the outermost backup seal can be provided with a porous wall, or filtering portion, through which the medium would have to pass before entering into and passing through the annulus.
2. Background Information
The known seal arrangements may offer sufficient protection against the penetration of coarse dirt particles into the annulus, but the protection is reduced when the dirt particles in question are fine particles which get sucked into the annulus on account of the underpressure which develops during rotation. Thus, these fine particles could enter into the vicinity of the ring seals.
German Patent No. 32 05 538 discloses seals for rotating shafts, which shafts have, in front of the ring seal, a plate which rotates along with the shaft. This rotating plate is equipped with pump elements which generate a circulating flow of the medium, and on the inflow side of the flow path of this circular flow, a porous layer is included. In this known system, however, the medium to be sealed out is not water bearing dirt and impurities, but is instead, an air-fluid mixture, in particular, an oil spray, such as that which occurs in the crankcase of an internal combustion engine. Accordingly, in this case the porous layer does not act to deflect dirt, but instead acts as a phase separator which separates the fluid phase from the gas phase of a gas-fluid mixture.